Selected papers from the second Krakow conference on Graph theory
Consistent query answers in inconsistent databases
PODS '99 Proceedings of the eighteenth ACM SIGMOD-SIGACT-SIGART symposium on Principles of database systems
Computing consistent query answers using conflict hypergraphs
Proceedings of the thirteenth ACM international conference on Information and knowledge management
ConQuer: a system for efficient querying over inconsistent databases
VLDB '05 Proceedings of the 31st international conference on Very large data bases
First-order query rewriting for inconsistent databases
Journal of Computer and System Sciences
Repair checking in inconsistent databases: algorithms and complexity
Proceedings of the 12th International Conference on Database Theory
On the consistent rewriting of conjunctive queries under primary key constraints
Information Systems
Minimal-change integrity maintenance using tuple deletions
Information and Computation
Proceedings of the twenty-ninth ACM SIGMOD-SIGACT-SIGART symposium on Principles of database systems
A remark on the complexity of consistent conjunctive query answering under primary key violations
Information Processing Letters
Consistent query answering: five easy pieces
ICDT'07 Proceedings of the 11th international conference on Database Theory
FQAS'11 Proceedings of the 9th international conference on Flexible Query Answering Systems
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The consistent query answering framework has received considerable attention since it was first introduced as an alternative to coping with inconsistent databases. The framework was defined based on two notions: repairs and consistent query answers. Informally, a repair is a consistent database that minimally differs from the inconsistent database. The consistent answers to a query are those tuples that appear in the intersection of the answer sets of the query when evaluated over all possible repairs. Here we study the complexity of the problem of consistent query answering for the class of acyclic conjunctive queries without self-joins, under primary key constraints. The problem is known to be coNP-complete in general for this class. Our goal is to determine the boundary between tractability and intractability, by establishing a dichotomy to the effect that, every conjunctive query in this class is either in PTIME or coNP-complete. In the PTIME direction, previous work has identified the queries for which consistent answers can be computed via first-order rewriting. In fact, for the class of acyclic conjunctive queries without self-joins, under primary key constraints, the boundary between first-order rewritable and not first-order rewritable queries has already been determined. Hence, our focus is on queries for which there is no first-order rewriting. We present a technique for computing in polynomial time the consistent query answers to several not first-order rewritable queries. We hope this technique may lay the foundations for a more general algorithm that handles all PTIME not first-order rewritable queries. In the hardness direction, we identify several representative queries of the class, for which we show that the problem is coNP-hard. This work is done under the supervision of Prof. Phokion G. Kolaitis and Prof. Wang-Chiew Tan.